Blue-collar workers are nearly twice as likely to be current smokers as white-collar workers, and this gap has been widening over time. Though they make as many quit attempts per year as their white-collar counterparts, blue-collar workers are less likely to succeed. Effective interventions applied in community-based channels that reach blue-collar workers are needed to reduce this growing disparity. Building trade unions are a potentially important, but largely unevaluated, channel for intervening with this population to reduce smoking prevalence. The proposed study builds upon our recently-completed pilot study in collaboration with 3 building trade union apprenticeship programs aimed at assessing smoking behaviors and determining the feasibility and effect size of a smoking cessation intervention. Pilot study results confirm that this population of workers is at very high risk of smoking (43% prevalence), that building trade unions can be recruited to a smoking cessation trial, and that our planned interventions are feasible and result in positive changes in smoking behavior. The proposed study uses a cluster randomized clinical trial study design to assess: (1) the efficacy of a smoking cessation intervention among unionized apprentices in the building trades; (2) the determinants of smoking cessation; and (3) the adoption (recruitment into the trial) among eligible apprenticeship programs, reach of the intervention among potential participants, elements of successful implementation and best processes of intervention activities delivered; and cost-effectiveness of the intervention. The intervention is based on prominent behavioral theories, empirical evidence from the peer-reviewed literature, and the US Public Health Service's guideline on smoking cessation, and it taps into essential elements of union culture. It will consist of: a toxics and tobacco curriculum module that includes information about disaster-related threats; group-based behavioral counseling; nicotine replacement therapy; do-it-yourself quit-kits; environmental cues for cessation; and written materials and quit groups for co-workers, friends, and family members. The study is innovative in its approach to intervening through building trade unions. If shown to be effective, this intervention could be readily disseminated to a national network of building trade union apprenticeship programs, which collectively train approximately 183,000 apprentices each year.